Relation between short-range order and crystallization behavior in Zr-based amorphous alloys

We have examined the effect of Ti and cooling rate on the crystallization o f Zr62-xTixCu20Ni8Al10(0 less than or equal to x less than or equal to 10) amorphous alloys. Ti stabilizes an icosahedral phase in Zr62-xTixCu20Ni8Al1 0(0 less than or equal to x less than or equal to 10) alloys. Without Ti (x =0), crystallization produces cubic and tetragonal intermetallic phases, an d the crystallization temperature shows no dependence on the cooling rate a t which the amorphous alloy was produced. The alloys containing Ti (3 less than or equal to x less than or equal to 10) precipitate an icosahedral qua sicrystalline phase upon annealing, and show a significant reduction of cry stallization temperatures with decreasing cooling rates of casting. We prop ose that the undercooled melts and amorphous alloys have icosahedral short- range order. The degree of short-range order or medium-range order in the a morphous alloys increases with decreasing cooling rate. Crystallization is easier when the precipitating phase resembles the short-range order of the amorphous solid. Therefore, the crystallization temperature is reduced when the precipitates are icosahedral. The dissimilarity between the structures of the precipitates and the short-range order in amorphous Zr62Cu20Ni8Al10 may be one of the reasons for its very wide supercooled liquid region. (C) 2000 American Institute of Physics. [S0003-6951(00)04739-2].